In the book, Leijonhufvud argued that John Hicks' IS/LM (Investment—Saving / Liquidity preference—Money supply) formulation of Keynes General Theory
was inadequate as an explanation for the "involuntary unemployment" in
John Maynard Keynes's writings. Rather, Leijonhufvud's reading of Keynes
emphasizes disequilibrium phenomena, which can't be addressed in the
IS/LM framework, as central to Keynes explanation of unemployment and economic depression.
Leijonhufvud used this observation as a point of departure to advocate a
"cybernetic" approach to macroeconomics where the algorithm by which
prices and quantities adjust is explicitly specified allowing the
dynamic economy to be studied without imposing the standard Walrasian
equilibrium concept. In particular, Leijonhufvud advocated formally
modelling the process by which information moves through the economy. While the "cybernetic" approach may have failed to gain traction in mainstream economics, it presaged the rational expectations revolution that would ultimately supplant the IS/LM model as the dominant paradigm in academic macroeconomics.